With known apparatus for manufacturing ventilation ducts and the like, a series of bends are made in a metal web to form a duct blank. The duct blank then is closed by one or more seams extending the length of the duct blank. The seams can be folded or welded shut.
A seam can be pre-formed by bending and aligning free edges of the partially formed duct. However, known seams must be clamped, backstopped, or otherwise supported from an inner surface of the duct blank in order to properly apply the forces required for adequate closure. Such clamping is not easily provided in-line with apparatus for bending the duct blank. Thus, the duct blank typically is removed from the bending apparatus to another work station for final closure of the seam. Removal of the duct blank to the other work station requires extra steps for handling and aligning the duct blank in the other work station. These extra steps reduce the efficiency of production.
Once the duct blank is removed from the bending apparatus, the seam can be closed by repeatedly banging a hammer against the free edge of the seam. However, the repeated impacts of the hammer are noisy and tend to deform the metal along the seam. Alternatively, Welty (U.S. Pat. No. 5,189,784 hereby incorporated herein by reference in its entirety) discloses an apparatus for forming and closing seams in box-shaped ducts. However, Welty's apparatus is not adapted for use in-line with other machinery. In particular, manual handling is required to properly position a duct blank relative to Welty's clamps and rollers. Thus, Welty's apparatus, although a significant advance in the art of its day, fails to optimize efficiency of production.